Integrated metabolomic and nutritional profiling reveals salinity-associated changes in muscle nutritional composition and metabolic responses in the swimming crab Portunus trituberculatus

Salinity profoundly influences the nutritional composition and metabolic physiology of crustaceans. Here, Portunus trituberculatus were cultured under low (18‰), normal (28‰), and high (38‰) salinities to evaluate changes in muscle nutrients and metabolites. Low salinity significantly increased muscle moisture content (77.20 vs. 76.37 g/100 g) but reduced protein content (19.07 vs. 19.43 g/100 g), while astaxanthin content increased markedly to 0.0413 mg/kg, nearly twice that of the normal salinity (0.0223 mg/kg). Amino acid analysis showed that low salinity significantly decreased Asp (1.1233 vs. 1.2667 g/100 g) and Thr (0.5167 vs. 0.5833 g/100 g), whereas high salinity increased Gly content (1.2033 vs. 0.9500 g/100 g), indicating that salinity may alter the amino acid composition. UHPLC–MS/MS metabolomics identified salinity-driven alterations in amino acid metabolism, lipid remodeling, and antioxidant pathways. Correlation analysis linked nutritional traits and key amino acids (Asp, Gly, Thr) with acylcarnitines, phospholipids, and phenolics, suggesting coordinated metabolic reprogramming under osmotic stress. Overall, these findings indicate that salinity alters muscle composition and amino acid profiles in P. trituberculatus and provide a metabolomic framework for future studies on salinity-responsive quality traits.